1. Field of the Invention
The present invention relates to the field of medical methods and devices, more specifically to medical angioplasty balloon catheters and devices intended to deliver active substances to body tissue.
Angioplasty balloons are one of the most commonly used tools for the treatment of narrowed blood vessels. These balloons are typically cylindrical when inflated and have different lengths and diameters to conform to different vessel sizes. The balloons are located at the distal end of flexible catheters and delivered to a target site/lesion where they are inflated at high pressure, normally between 8-20 atmospheres, in order to overcome the resistance of the lesion and achieve luminal expansion. Such high pressure angioplasty is often associated with trauma to the vessel walls with a resulting high frequency of vessel dissection (30%-40%), abrupt closure of the treated vessel (5%-12%), and restenosis. Thus, when conventional angioplasty is used as a primary treatment for occluded vessels, restenosis can occur in about 50% of the cases. Therefore, in the vast majority of coronary treatments, angioplasty is used as an initial treatment followed by placement of a stents. Frequently, the stents are coated with drug and polymer requiring the patient to take anti platelet therapy for extended periods, possibly lifelong. to limit the risk of stent thrombosis or blood clots. Anti platelet therapy increases the risk of bleeding and is expensive. In addition, patient must stop the antiplatelet therapy before any surgical intervention, thus increasing the risk of sudden death and often precluding beneficial procedures.
Dissections in blood vessels treated by balloon angioplasty are very common. The dissection rate is estimated to be as high as 30% of all cases. Some of the dissections are severe and may require urgent surgery or placement of additional stents. In addition, dissection may contribute to poor long term clinical results and restenosis even if a stent is placed in the treated lesion. Dissections are usually attributed to several mechanisms occurring during balloon inflation including shear forces applied on the vessel walls as the balloon pleats unfold as well as the uneven balloon inflation which occurs as a result of the non-symmetric nature of the vascular disease. During inflation, the balloon diameter increases in the radial direction as the folded balloon unwraps. As the folded lobes of the balloon open, the layers slide over one another and apply tangential forces to the lesion and/or vessel wall which can abrade the lesion or vascular wall and in the worst instances cause dissections. As shown in FIGS. 1A-1C, a catheter 10 is initially located in a region of plaque (P) in a blood vessel (BV). A balloon 12 on the catheter 10 has folded lobes which unfold as the balloon is inflated, as shown in FIG. 1B. The layers of the folded lobes move in opposite directions, as shown by the arrows in FIG. 1B, with the upper exposed layer tending to slide across the surface of the lesion or if present, exposed vascular wall. Such unintended lateral movement of the balloon surface can occur until the balloon is fully inflated, as shown in FIG. 1C.
Uneven inflation results from the uneven nature of the disease in the vessel. Angioplasty balloons are commonly non-compliant or semi-compliant, and when semi-compliant balloons are inflated against an eccentric lesion, the balloon will follow the “path of least resistance” and its diameter will increase more in the less diseased sections of the vessel, often increasing trauma in these areas.
For these reasons, it would be desirable to provide improved balloons and inflation structures for angioplasty balloons used in vascular treatments. In particular, it would be desirable to provide angioplasty balloons having a reduced tendency to cause trauma and dissection in the blood vessel walls as the balloon is inflated by modulating the inflation characteristics of the balloon and provide a segmented compartmental dilatation with local areas of compliance. It would be further desirable if the reduced dissections could also reduce the risk of elastic recoil and abrupt reclosure which are associated with current angioplasty balloons and their use. It would be further desired if such improved angioplasty balloon structures were compatible with each of stents, drug-eluting stents, and drug coated balloons. These advantages would preferably be obtained without loss of the ability of the catheters to increase the luminal size and restore blood vessel in the patient being treated. At least some of these objectives will be met by the invention as described hereinafter.
2. Description of the Background Art
U.S. Pat. Nos. 6,245,040 and 5,735,816, show balloon catheters having elastic spiral restraints which form spiral indentations in the balloon when inflated. Other patents of interest include U.S. Pat. Nos. 7,708,748; 7,686,824; 5,863,284; 5,772,681; 5,643,210; and 5,987,661.